EFFECT OF MATERNALLY ACQUIRED AUJESZKYS-DISEASE (PSEUDORABIES) VIRUS-SPECIFIC ANTIBODY IN PIGS ON ESTABLISHMENT OF LATENCY AND SEROCONVERSION TO DIFFERENTIAL GLYCOPROTEINS AFTER LOW-DOSE CHALLENGE

This study investigated whether (1) passively immune pigs could become latently infected after challenge with low doses of wild type pseudor abies virus (PRV) and (2) if seroconversion to PRV could be consistent ly detected using two commercially available differential diagnostic E LISAs. Three litters of piglets with passively acquired PRV serum neut ralizing (SN) antibody (geometric mean titers 47.03 to 95.10) were cha llenged at 6 to 12 days of age with 236 to 500 TCID50 of Shope strain virus; pigs were vaccinated at 11 weeks of age with a commercially ava ilable genetically engineered vaccine (TK(-)gE(-)gG(-) Iowa S62 strain PRV). Vaccination was intended to reduce the risk of reactivation of latent infection resulting in spread of virulent PRV infection to prev iously uninfected pigs during the experiment. Vaccination at this age also approximated common field practices in infected herds. After 15 w eeks, all challenged pigs were seropositive on the PRV glycoprotein (g or gp) E differential ELISA but were seronegative on the gG different ial ELISA. All three challenge groups had pigs that were latently infe cted as evidenced by the detection of PRV DNA by polymerase chain reac tion (PCR) assay of their trigeminal ganglia (TG). There was a signifi cant inverse relationship observed for age at challenge and the propor tion of PCR positive pigs in the group 15 weeks postchallenge (p=0.000 4). This trend was independent of the passively acquired PRV SN antibo dy titers at challenge. In this study, passively acquired antibody did not provide protection against establishment of latent infection in p iglets after exposure to low doses of virulent PRV. These latent infec tions were detected serologically by only one of two available differe ntial diagnostic ELISAs. (C) 1997 Elsevier Science B.V.